Bimetal brake drum



April 4, 1961 T. c. soDDY BIMETAL BRAKE DRUM Filed April 1, 1957 UnitedStates Patent" i ce BIMETAL BRAKE DRUM Thomas C. Soddy Chicago, lll.,assignor to Chicago Railway Equipment Company, Chicago, Ill., acorporation of Illinois v f 4 v Y Filed Apr; 1, 1957, ser. Ne. 649,902

6 elaimsl-` (cl. v18s-,4218) The invention relates to brake drums,` andparticularly to drums of the type used on vehicles in which ashoecontacting liner having a high coefficient of friction andV highwear resistance, such as iron or steel, is embedded in a relativelyheavy housing of a lighter metal having higher heat conductingcharacteristics, such as aluminum or an alloy thereof.

Brake drums of this type are intended to obtain the friction-resistancewear qualities of a ferrous metal with the light weight and highheat-conductive properties of aluminum, magnesium or other metals low inthe scale of specific gravity. In drums of this type as previouslyconstructed, the housing of light metal has been cast around insertsofrferrous metal, but the high heat dissipation during heavy braking,which must be absorbed by the drum since the brake shoe is usually madeof a heat insulator material, causes a fading or drop in the coeicientof friction between the drum and the brake shoe because ofthe loweringof the tensile strength of the drum as the temperature rises. The use ofa housing or muiikformed of aluminum, for the iron liner has beenproposed because aluminum has approximately two and one-third times thecoeicient of heat transfer relative to iron, but to utilize thecharacteristics of the aluminum housing, it is essential that there bemaintained an extended close contact between the iron and aluminumcomponents and that the iron elements cannot work loose from thealuminum housing elements. Attempts to maintain such close contact havenot been satisfactorily effected because of the different coefficientsof expansion of the iron and aluminum parts. Also, there is a tendencyof the drum to ovate, which results in uneven load concentration on thebrake shoes and therefore an undue rise e in temperature.

The present invention relates to overcoming the disadvantages previouslyencountered, and consists primarily in providing a continuous helix offerrous metal for contact with the brake shoes and substantiallyembedding the helix convolutions, which are spaced apart, in thealuminum or other light metal muli r housing throughout the length ofthe helix for substantially the full depth of the convolutions.

Illustrative embodiments of the invention are shown in the accompanyingdrawings, in which:

Figure 1 is a vertical longitudinal section through a -bimetal drumembodying one form of the invention; the upper portion of the gure showsthe drum as it comes Qigfrom the mold, and the lower portion of thefigure shows #the drum after a portion of its inner periphery has beenmachined away to produce a thinner and smoother liner. Figure 2 is aside elevation of the ferrous metal helical liner before it isincorporated in the drum housing as shown in Figure l.

Figure 3 is in part a right hand elevation of the drum l shown in Figure1, and in part (indicated by the arrow 3a) a section on line 3a3a ofFigure l; and in part (indicated by the arrow 3b) a section on line3b-3b of Figure 1. e

Patented Apr. 4, 1961 Figure 4 is a detail cross section through aportion of a similar section illustrating a fourth form of helix.

' Figure 7 is a sectioncorresponding to the upper por-Y tion of Figurel, but illustrating another form of liner casting about which thehousing metal has been cast.

The helix 1 (Figures 1-3) comprises a plurality of Y convolutions 2normally spaced apart and extending substantially throughout the lengthof the drum and forming the major portion of the inner periphery of thedrum. Preferably, each' convolution has a relatively narrow rib 3projecting from its outer periphery and extending substantiallycontinuously of the helix.

The helix is formed of ferrous metal, and a preferred form of the helixis a gray iron casting which may be cast as shown. Also, the helix stripcould be formed initially of a continuous rolled section andlsubsequently curved about a mandrel to form the helix.

'The housing 4 is formed of aluminum, magnesium or other metal ofsubstantially lower specific gravity and higher heat conductivity thaniron, preferablybelow 3 in the scale of specific gravity. The housing iscast about the helix, and prefer-ably is molecularly bonded thereto. Onemethodl of bonding is byv dipping the helix into a molten bath'ofiron-aluminum alloy before the housing metal ispoured, as described inWhitfield et al. Patent No. 2,396,730. Irrespective of the bonding, thealuminum is in close contact with the outer periphery of the helix andwith the annular faces 5 of the helix, and is between successiveconvolutions of the helix and thus contributes to the rapid dissipation`of heat and avoids the building up of high temperatures which reducethe frictional characteristics of the iron which would permit the brakeshoes to slip over the liner and thereby increase the temperature andlower the tensile strength of the drum. Additional dissipation of heatwithout undue weakening of the drum is obtained by providingasubstantially continuous groove 6 in the housing intermediate theconvolutions of the helix. The ends of the helix, at 7, abut the castmetal of the housing. These abutting ends and the inclination of theconvolutions anchor the lining against any rotary shifting within thehousing even though the bond should fail. Accordingly the iron insertcannot work loose from the housing metal and decrease the dissipation offrictional heat from the lining. Ribs 3 increase the radiant surfaceapproximately one hundred percent, and similarly increase theinterfacial bond between the iron and aluminum. Due to the helix design,the forces applied to the interfacial bond are distributed by combinedstresses through tension, compression shear and torsion through theentire length of the helix, and the difference in the coeiicient ofexpansion between the liner and housing is more effectively distributedbecause of the shape of the cross section of the liner. The provision ofribs 3 also reinforces the drum transversely and better resists theovating of the drum under heavy loads. The helix provides for frictionalcontact with the shoes throughout their length and thus avoids cuttingor grooving of the shoes.

Figure 4 illustrates a cross section of a helix strip 12 in which thesides 12a of the strip are inclined to the axis of the helix and housing13, and thus provide an additional locking means for tbe liner in thehousing.

Figure 5 shows another cross section for a helix 22 in which the sides23a of the rib 23 are inclined similar to the sides 12a shown in Figure4.

Figure 6 shows another cross section for a helix 32 in which there isprovided a pair of ribs 33 at the sides 3 of the helix, thus increasingthe depth of the helix sides 32a which are inclined similar to the sides12a of the helix shown in Figure 4.

Each form of helix shown in Figures 4, 5 and 6 would be restrictednecessarily to rolled sections formed into a helix, because it is notfeasible to make a casting with the draft shown as a result of theinclination of the sides of the helix to the helix axis. Y

Figure 7 illustrates a drum in which the helical liner is cast initiallywith the successive convolutions 42 united, at least adjacent the innerperiphery of the casting. The housing 44 is then cast about the linerconvolutions 42 and ribs 43 and the inner periphery of the bimetal drumis machined down to the line indicated at X, producing a nished vproductsubstantially like that shown in Figure 1. In this structure the initialcasting of the liner is simpler than that shown in Figure 2. An evenmore simple structure would be to utilize a cylinder with strenght innerand outer sides and machine it down to the form shown in Figure 7. Withsuch an arrangement, the initial liner could be either cast metal orforged metal.

Each of the structures described attains the objectives set forth in theintroductory portion of the specification. The details may be variedother than as described without departing from the spirit of theinvention and the exclusive use of those modifications coming within thescope of the claims is contemplated.

What is claimed is:

1. A bimetal brake drum comprising a rigid housing of a metal havinghigh heat conductivity characteristics having a continuous peripheralcircumferential Wall, a helix of metal having an inner face, an outerface, and side faces, the coils of said helix being spaced apartlengthwise of the helix axis and wherein the outer face and at least aportion of said side faces are embedded fixedly within said housingwall, the said coils being maintained in spaced relationship by acontinuous helical rib formed as an integral part of said housing wallextending between said coils, the said inner face of said helix forminga continuously circular brake-shoe contacting surface for the drum.

s2. A bimetal brake drum comprising a rigid housing of a metal havinghigh heat conductivity characteristics having a continuous peripheralcircumferential wall, a helix of metal having an inner face, an outerface and Side faces, the coils if Said helix being spaced apart.

lengthwise of the helix axis and wherein the outer face and at least aportion of said side faces are embedded within said housing wall, thesaid coils being maintained in spaced relationship by a continuoushelical rib formed 4 as an integral part of said housing wall extendingbetween said coils, said helix having an elongated helical rib on itsouter periphery and wherein the outer periphery of said housing wallsurrounding the helix is grooved helically intermediate the convolutionsof said helical rib, the said inner face of said helix forming acontinuously circular brake-shoe contacting surface for the drum.

3. A bimetal brakeY drum comprising a rigid housing of a metal havinghigh heat conductivity characteristics having a continuous periphehalcircumferential wall, a helix of metal having an inner face, an outerface, and side faces, said helix and housing having differentcoefficients ofexpansion, theA coils of said helix being spaced apartlengthwise of the helix axis and wherein the outer face and at least aportion of said side faces are embedded within said housing wall, thesaid coils being maintained in spaced relationship by a. continuoushelical rib formed as an integral part of said housing wall extendingbetween said coils, the said inner face of said helix forming acontinuously circular brake-shoe contacting surface for the drum, andanchoring means formed as an integral part of said helix includingsurfaces inclined relative to the axis of the helix and housing andserving to anchor said helix to said housing wall.

4. A structure as defined in claim 3, wherein the anchoring meanscomprise the inclination of the sides of said helix to the axis of thehelix and housing.

5. A structure as defined in claim 4, wherein the inclined sides of thehelix extend beyond the inner face of said helix.

6. A structure as defined in claim 3, wherein the anchoring meanscomprises a rib having an outer face and side faces, the side faces ofsaid rib being inclined to the axis of the helix and the housing.

References Cited in the tile of this patent UNITED STATES PATENTS1,010,789 Nilson Dec. 5, 1911 1,394,402 Birkigt Oct. 18, 1921 1,989,211Norton Jan. 29, 1935 2,062,394 Brown Dec. 1, 1936 2,105,323 Hunt Jan.1l, 1938 2,292,662 Sanders Aug. 11, 194'2 2,382,570 Kraft Aug. 14, 19452,462,139 Sparkes Feb. 22, 1949 2,840,195 Holton June 24, 1958 FOREIGNPATENTS 560,903 Great Britain Apr. 26, 1944 557,866 Italy Feb. V21, 1957

